limit outgoing baud rate

I have been mostly successful sending faxes over SIP but sometimes some faxes fail. I suspect that 14400 baud is not a good idea. Is it possible to force an upper limit say 9600 baud for outgoing faxes on hylafax? Where do I set it?

Other thought is that if I am getting incoming fax on IAXmodem while I am sending out a fax it might get interrupted. Is there way to route outgoing fax to use certain IAXmodem?